We propose to investigate the acute effects of several socially-abused drugs (secobarbital, methamphetamine, diazepam, and meperidine hydrochloride) on specific aspects of human information processing. We will study drug effects in healthy subjects serving as their own controls with specific reference to cognitive changes that affect the performance of everyday tasks and that may contribute to the abuse-potential of the drugs. Behavioral and neurophysiological tests designed to investigate attention, memory, probability-learning, and self-evaluation of performance will be applied. Particular emphasis will be placed on using tests which enable a determination of the specific stage or aspect of information processing which is most sensitive to the effects of particular drugs. For example, are drug-induced changes in performance due to changes in selective attention, short-term storage capacity, rate of transfer from short-term to long-term store, or retrieval? Is semantic memory or immediate memory more sensitive to drug effects? Is recall more sensitive than recognition? Event-related potentials will be calculated from the electroencephalograms recorded during performance of several of the cognitive tasks to provide neural correlates of behavioral responses.